The present invention relates to a sizing composition used in glass fiber reinforced resin and plastic articles and to selected synthetic organosilane lubricants incorporated therein.
It is well known to use glass fibers to reinforce polymeric materials. These glass fibers are provided in various forms such as mats including chopped strand mats and continuous strand mats; rovings which are bundles of glass fiber strands wound up in parallel, i.e. without twist; woven rovings; and chopped and milled fibers. They are produced by a process called forming wherein fibers are drawn at a high rate of speed from molten glass through tiny orifices or tips in a heated platinum bushing (a fiber-drawing furnace) then attenuated into a multi-filament strand. The glass fibers so produced must be protected from interfilament abrasion during formation and processing and must be made compatible with the polymeric materials they are to reinforce. This is usually accomplished by treating the glass fibers with a sizing composition.
Basically, a fiber size must provide the following characteristics to the strand of filaments: a) good adhesion between glass fiber and polymer; b) good cohesion between filaments within a strand; c) certain handling characteristics like hardness, softness, choppability, etc. imparted by careful selection in terms of type and quantity of components; d) protection of the strand during its various processing stages and e) other desired characteristics such as antistatic and electrical properties.
Sizing compositions are well known in the art and include the starch based sizes used in the formation of glass fiber weavers yarns and fiber sizes designed for the reinforcement of thermosetting resins and thermoplastics. The latter type sizes, sometimes referred to as plastics size, typically comprising a film-forming polymeric or resinous component, a coupling or keying agent and a lubricant. The majority of fiber sizes for general purpose reinforcing materials use polyvinyl acetate as a film-former, Polyesters, epoxides, polymethyl methacrylate and polystyrene are also used as film-formers, sometimes alone and sometimes as copolymers or blends with polyvinyl acetate. Coupling or keying agents (also called adhesion promotors) improve the bond between the polymeric resin and glass and typically are organo-metallic, in most cases organo-silicon compounds. Common lubricants used are cationic surface-active agents such as a fatty acid amine or a fatty acid quaternary ammonium compound.
Many different sizing compositions, having formulations which are adapted to provide the various properties desired in the glass fiber products, have been developed. Typical compositions are disclosed in "The Manufacturing Technology of Continuous Glass Fibers" by K. L. Lowenstein, second edition, Elsevier Science Publishing Company, 1983 wherein a number of film formers, coupling or keying agents, lubricants and other components such as plasticisers, emulsifiers, antistatic agents and miscellaneous other materials are disclosed. More specific glass fiber sizing compositions are disclosed in the following patents. In U.S. Pat. No. 3,865,768 issued Feb. 11, 1975, a glass sizing composition to provide lubricity in the formation of rovings and which is a compatible with polyester resins is disclosed and comprises a poly (vinyl acetate) latex film former, a polyester compatible silane, at least one alkyl amide reaction product of an alkyl carboxylic acid and an ethylene amine and a nonionic surfactant derived from halogentated fatty acid containing oil. U.S. Pat. No. 3,933,711 issued Jan. 20, 1976 discloses an aqueous sizing composition comprising polyvinyl acetate, a fatty acid amide lubricant, methacrylate chronic chloride and gamma (ethylene diamine) propyl trimethoxy silane. U.S. Pat. No. 4,284,538 issued Aug. 18, 1981 discloses an aqueous dispersion sizing composition containing a cationic imidazoline; an aliphatic aromatic and/or polymeric ester and polyethylene.
Other sizing compositions are disclosed in U.S. Pat. No. 4,341,877 issued Jul. 27, 1982 which shows a composition comprising an epoxidized polar thermoplastic copolymer, an organosilane coupling agent and a nonionic, cationic or anionic lubricant and in U.S. Pat. No. 4,448,910 issued May 15, 1984 wherein the composition includes an emulsified epoxy resin and 3-chloropropyltrimethoxy silane as the coupling agent. U.S. Pat. No. 4,489,131 issued Dec. 18, 1984 discloses a size for glass fibers employed in reinforcing polypropylene comprising an oxidized polyolefin, a carboxylated high molecular weight elastomer as a film former, an amino silane and a selected organic acid.
In producing glass reinforced fibers, as disclosed above, many different sizing compositions have been used. While lubricants to aid in the processibility of the glass fibers are generally used, in many instances they can have a detrimental effect on same properties. For example, they reduce the strength and stiffness of a glass reinforced product.
Accordingly, there is the need for a sizing composition, for use in producing glass fiber reinforced articles, which contains a lubricant and which has improved strength and stiffness properties.